[The capacitation of spermatozoa]

Mammalian spermatozoa attain their fertilization capacity only after reaching the female genital tract. This process takes place in several stages. First there is a degradation of inhibitors (decapacitation factor and acrosin inhibitor) in the vagina, cervix and uterus. Concurrent with or subsequent to this process the actual capacitation in the uterus and tubes occurs. Capacitation is characterized by an increase in metabolism, alteration of motility and activation of lytic enzymes of the spermatozoa. The acrosome reaction takes place only on direct contact with the ovum. This reaction is accompanied by morphological changes in the spermatozoon and enables the proteolytic enzymes (corona-penetrating enzyme, acrosin and hyaluronidase) to leave the sperm head. With the help of these enzymes, the spermatozoon is able to break down the various egg envelopes, to penetrate the ovum and initiate fertilization.